1. Field of the Invention
The present invention relates to a gateway device, a radio base station device, a router device and a radio terminal device, which are to be used in radio communications utilizing the transport layer.
2. Description of the Background Art
In recent years there are increasing demands for carrying out not just speech communications but also data communications by radio. TCP (Transmission Control Protocol) is widely used as a reliable transport layer protocol in the wire data communications, but the direct application of this protocol to radio communications causes the following problems.
A TCP segment loss in the wire communications implies the congestion of a network so that TCP is designed to avoid the congestion by lowering a data transmission rate when the segment loss is detected. For this reason, the TCP segment loss due to a radio section error and a handoff will also be interpreted as the congestion so that the congestion avoidance operations will be executed more than necessary and as a result the throughput will be lowered more than necessary.
In order to resolve this problem, there is a proposition to use the usual TCP in a wire network and the radio transport layer in a radio network and relay communications at a border between the wire network and the radio network. For example, “selective ack” is used for a high segment loss rate on the radio network side. Namely, this is a scheme for resolving the congestion problem in such a way that a data loss in the radio section is not regarded as the congestion and a re-transmission is carried out without lowering the transmission rate.
Also, in TCP, when an idle connection state, i.e., a state where no response comes from a terminal on one side and no response comes a terminal on the other side as well, is continued for two hours, a keep-alive packet will be transmitted by a server terminal in which a keep-alive option is set valid. If there is no response to this keep-alive packet which is an inspection packet, the transmission of this keep-alive packet will be continued at 75 seconds interval, but when ten consecutive trials fail, it is judged that a terminal on the client side is inactive and the connection will be disconnected.
As described, in the case of carrying out communications between a radio terminal device accommodated in a radio network and a wire terminal device accommodated in a wire network, the radio terminal and a gateway device for relaying the transport layer protocol cannot directly ascertain the radio communication state of the radio terminal that terminates the transport layer connection, so that there has been a problem that it is impossible realize the adaptive control of the transport layer connection (such as a dynamic change of a segment size) according to the radio communication state or property.